写在前面
这个demo来说明怎么一步步排查一个常见的spring boot AutoConfiguration的错误。
https://github.com/hengyunabc/spring-boot-inside/tree/master/demo-database-type-NONE
调试排查 Cannot determine embedded database driver class for database type NONE 的错误
把工程导入IDE里，直接启动应用，抛出来的异常信息是：
Error starting ApplicationContext. To display the auto-configuration report re-run your application with 'debug' enabled.
2017-11-29 14:26:34.478 ERROR 29736 --- [ main] o.s.b.d.LoggingFailureAnalysisReporter :
***************************
APPLICATION FAILED TO START
***************************
Description:
Cannot determine embedded database driver class for database type NONE
Action:
If you want an embedded database please put a supported one on the classpath. If you have database settings to be loaded from a particular profile you may need to active it (no profiles are currently active).
其实这时有两个思路，直接google搜索Cannot determine embedded database driver class for database type NONE，就可以找到解决办法。
第二种方式，仔细查看日志内容，可以发现有To display the auto-configuration report re-run your application with 'debug' enabled.。
搜索下这个，就可以在spring的官方网站上找到相关的信息：https://docs.spring.io/spring-boot/docs/current/reference/html/using-boot-auto-configuration.html
就是用户只要配置了debug这个开关，就会把auto-configuration 相关的信息打印出来。
熟悉spring的环境变量注入的话，就可以知道有几种打开这个的方式：
- 在
args里增加--debug - 在application.properties里增加
debug=true - 通过
-Ddebug=true
增加debug开关之后的信息
增加debug开关之后，可以看到打印出了错误堆栈：
2017-11-29 14:33:08.776 DEBUG 29907 --- [ main] o.s.b.d.LoggingFailureAnalysisReporter : Application failed to start due to an exception
org.springframework.boot.autoconfigure.jdbc.DataSourceProperties$DataSourceBeanCreationException: Cannot determine embedded database driver class for database type NONE. If you want an embedded database please put a supported one on the classpath. If you have database settings to be loaded from a particular profile you may need to active it (no profiles are currently active).
at org.springframework.boot.autoconfigure.jdbc.DataSourceProperties.determineDriverClassName(DataSourceProperties.java:245) ~[spring-boot-autoconfigure-1.4.7.RELEASE.jar:1.4.7.RELEASE]
at org.springframework.boot.autoconfigure.jdbc.DataSourceProperties.initializeDataSourceBuilder(DataSourceProperties.java:182) ~[spring-boot-autoconfigure-1.4.7.RELEASE.jar:1.4.7.RELEASE]
at org.springframework.boot.autoconfigure.jdbc.DataSourceConfiguration.createDataSource(DataSourceConfiguration.java:42) ~[spring-boot-autoconfigure-1.4.7.RELEASE.jar:1.4.7.RELEASE]
at org.springframework.boot.autoconfigure.jdbc.DataSourceConfiguration$Tomcat.dataSource(DataSourceConfiguration.java:53) ~[spring-boot-autoconfigure-1.4.7.RELEASE.jar:1.4.7.RELEASE]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_112]抛出异常的代码是：
/**
* Determine the driver to use based on this configuration and the environment.
* @return the driver to use
* @since 1.4.0
*/
public String determineDriverClassName() {
if (StringUtils.hasText(this.driverClassName)) {
Assert.state(driverClassIsLoadable(),
"Cannot load driver class: " + this.driverClassName);
return this.driverClassName;
}
String driverClassName = null;
if (StringUtils.hasText(this.url)) {
driverClassName = DatabaseDriver.fromJdbcUrl(this.url).getDriverClassName();
}
if (!StringUtils.hasText(driverClassName)) {
driverClassName = this.embeddedDatabaseConnection.getDriverClassName();
}
if (!StringUtils.hasText(driverClassName)) {
throw new DataSourceBeanCreationException(this.embeddedDatabaseConnection,
this.environment, "driver class");
}
return driverClassName;
}可以看出来是没有找到 DataSource 的driver class，然后抛出了 DataSourceBeanCreationException。
那么一种解决办法是，在maven依赖里加入一些 DataSource driver class。
但是应用自己的代码里并没有使用DataSource，哪里导致spring boot要创建一个DataSource对象？
哪里导致spring boot要创建DataSource
从异常栈上，可以找到DataSourceConfiguration$Tomcat 这个类，那么查找下它的引用，可以发现它是被org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration.PooledDataSourceConfiguration import引入的。
@Configuration
@Conditional(PooledDataSourceCondition.class)
@ConditionalOnMissingBean({ DataSource.class, XADataSource.class })
@Import({ DataSourceConfiguration.Tomcat.class, DataSourceConfiguration.Hikari.class,
DataSourceConfiguration.Dbcp.class, DataSourceConfiguration.Dbcp2.class,
DataSourceConfiguration.Generic.class })
protected static class PooledDataSourceConfiguration {
}那么 PooledDataSourceConfiguration 是怎么生效的呢？从代码上可以看到@Conditional(PooledDataSourceCondition.class)。
那么再看PooledDataSourceCondition的具体实现：
/**
* {@link AnyNestedCondition} that checks that either {@code spring.datasource.type}
* is set or {@link PooledDataSourceAvailableCondition} applies.
*/
static class PooledDataSourceCondition extends AnyNestedCondition {
PooledDataSourceCondition() {
super(ConfigurationPhase.PARSE_CONFIGURATION);
}
@ConditionalOnProperty(prefix = "spring.datasource", name = "type")
static class ExplicitType {
}
@Conditional(PooledDataSourceAvailableCondition.class)
static class PooledDataSourceAvailable {
}
}PooledDataSourceCondition引入了@Conditional(PooledDataSourceAvailableCondition.class) ：
/**
* {@link Condition} to test if a supported connection pool is available.
*/
static class PooledDataSourceAvailableCondition extends SpringBootCondition {
@Override
public ConditionOutcome getMatchOutcome(ConditionContext context,
AnnotatedTypeMetadata metadata) {
ConditionMessage.Builder message = ConditionMessage
.forCondition("PooledDataSource");
if (getDataSourceClassLoader(context) != null) {
return ConditionOutcome
.match(message.foundExactly("supported DataSource"));
}
return ConditionOutcome
.noMatch(message.didNotFind("supported DataSource").atAll());
}
/**
* Returns the class loader for the {@link DataSource} class. Used to ensure that
* the driver class can actually be loaded by the data source.
* @param context the condition context
* @return the class loader
*/
private ClassLoader getDataSourceClassLoader(ConditionContext context) {
Class<?> dataSourceClass = new DataSourceBuilder(context.getClassLoader())
.findType();
return (dataSourceClass == null ? null : dataSourceClass.getClassLoader());
}
}从代码里，可以看到是尝试查找dataSourceClass，如果找到，条件就成立。那么debug下，可以发现查找到的dataSourceClass是：org.apache.tomcat.jdbc.pool.DataSource 。
那么再看下org.apache.tomcat.jdbc.pool.DataSource这个类是从哪里来的呢？
从maven依赖树可以看到，依赖是来自：spring-boot-starter-jdbc。所以是应用依赖了spring-boot-starter-jdbc，但是并没有配置DataSource引起的问题。
问题解决办法
有两种：
- 没有使用到
DataSource，则可以把spring-boot-starter-jdbc的依赖去掉，这样就不会触发spring boot相关的代码 - 把spring boot自动初始化
DataSource相关的代码禁止掉
禁止的办法有两种：
-
在main函数上配置exclude
@SpringBootApplication(exclude = { DataSourceAutoConfiguration.class, DataSourceTransactionManagerAutoConfiguration.class }) -
在application.properties里配置：
spring.autoconfigure.exclude=org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration
总结
- 应用没有使用到
DataSource，但是在pom.xml里引入了spring-boot-starter-jdbc -
spring-boot-starter-jdbc带入了tomcat-jdbc，它里面有org.apache.tomcat.jdbc.pool.DataSource - spring boot里的
PooledDataSourceConfiguration，判断classpath下面有DataSource的实现类，尝试去创建DataSourcebean - 在初始化
DataSourceProperties时，尝试通过jdbc的url来探测driver class - 因为应用并没有配置url，所以最终在
DataSourceProperties.determineDriverClassName()里抛出Cannot determine embedded database driver class for database type NONE
最后：
- 排查spring boot的AutoConfiguration问题时，可以按异常栈，一层层排查
Configuration是怎么引入的，再排查Condition具体的判断代码。
